Background: Integration of engineering into middle school science and mathematics classrooms is a key aspect of STEM integration. However, successful pedagogies for teachers to use engineering talk in their classrooms are not fully understood. Purpose/Hypothesis: This study aims to address this need with the research question: How does a middle school life science teacher use engineering talk during an engineering design-based STEM integration unit? Design/Method: This case study examined the talk of a teacher whose students demonstrated high levels of learning in science and engineering throughout a three-year professional development program. Transcripts of whole-class verbal interactions for 18 class periods in the life science-based STEM integration unit were analyzed using a theoretical framework based on the Framework for Quality K-12 Engineering Education. Results: The teacher used talk to integrate engineering in a variety of ways, skillfully weaving engineering throughout the unit. He framed lessons around problem scoping, incorporated engineering ideas into scientific verbal interactions, and aligned individual lessons and the overall unit with the engineering design process. He stayed true to the context of the engineering challenge and treated the students as young engineers. Conclusions: This teacher's talk helped to integrate engineering with the science and mathematics content of the unit and modeled the practices of informed designers to help students learn engineering in the context of their science classroom. These findings have the potential to improve how educators and curricula developers utilize engineering teacher talk to support STEM integration.